


The Second Day of Gyftmas - Bite

by MageOfLight



Series: 12 Days of Gyftmas - 2017 [3]
Category: Undertale
Genre: Aftercare, Biting, Collars, Ecto-Genitalia, Established Dom/Sub dynamics, Fingering, M/M
Language: English
Status: Completed
Published: 2017-12-14
Updated: 2017-12-14
Packaged: 2019-02-14 17:33:21
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,595
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13012731
Author URL: https://archiveofourown.org/users/MageOfLight/pseuds/MageOfLight
Summary: UF!Sans and Classic Sans are in a long established dom/sub relationship and decide to experiment with a new kink.





	The Second Day of Gyftmas - Bite

**Author's Note:**

  * For [wolfbunny](https://archiveofourown.org/users/wolfbunny/gifts).



> so, i was given a ship (kustard) and a kink (biting) with no actual prompt... so i ran with what i wanted to do with it. hope it's satisfactory, wolfbunny! haha
> 
> it kinda wound up being very story driven, too... might mess with this universe later on my own time because i love dom/sub stuff but i've never written anything quite like this before. also, i realized this is probably my first kustard fic?! what is wrong with me, waiting so long?! O_O

Sans hummed softly along with the dumb Christmas songs playing on the radio as he waited in his basement lab that doubled as a play room.  
  
Since arriving on the surface ten years prior, his life had taken so many interesting and uplifting turns. The humans had been remarkably accepting of monsters coming out of the mountain (though monster tech and what they could offer the humans made everything go so much smoother), and they'd quickly established a community at the base of the mountain. That small town had grown and expanded so quickly with the addition of humans and the heightened birthrate of monster couples.  
  
It'd expanded further when a weird glitch in the universe had spat another set of monsters from the mountain, these ones looking like they'd gone through hell and back, being lead out by a small red-eyed human that could have been Frisk's twin and was, in fact, their alternate universe double.  
  
That had set the humans off, but they were quickly pacified by the second Frisk assuring them that despite their rough appearance, the second set of monsters were all good people. Curiosity from the scientific community quickly overpowered fear of the new monsters, and things smoothed out once again.  
  
There were less than half the monsters in the second set but their rough alternates were quickly accepted into the community, the originals doing their best to help the new monsters settle in. Sans had invited his own universal twin and his brother to stay with them, though the other Sans who they'd renamed Red was the only one to accept the offer. The other Papyrus, who they called Edge, decided he'd rather not settle, desiring to make use of his new found freedom to travel.  
  
And over the course of that time of change and adjustment, Sans had found himself healing from years of pain. The addition of Red into his life just hastened the process. Sans had recovered his spark, much to Papyrus' delight. He felt happy and content, his HOPE having raised from the single point it had fallen to over the course of Flowey's bullshit and Frisk's multiple resets to a stable 20 points, more than enough to abate Papyrus' constant worry.  
  
He got back into science, finding himself working with Alphys and her alternate, who'd changed her name to Alli, though Red declined to join them himself and enjoyed messing around in the lab in their basement instead.  
  
Granted, most of his experiments resulted in... interesting situations. That was how they'd first fell ass over tea kettle into a relationship with each other. It had started as a blatantly sexual experiment, Sans submitting himself to being Red's test subject when Red begged him. Their occasional experiment had evolved into a full-on dom/sub dynamic when Sans revealed one day that he trusted Red explicitly. Red had been floored and then overjoyed to know that he'd earned Sans' trust, and their experiments had shifted to play that had slowly grown more intense over time.  
  
Their relationship had become stable, though it was still entirely sexual in nature, Sans too nervous to tell Red just how deep his feelings for him went. How do you even tell someone that you've fallen in love with them after you've been fucking for nearly two years? There was no real commitment between them other than the rules that they kept to with their play, and as much as Sans wanted the romantic aspect with his dom, he didn't want to risk ruining what they already had, either. It was comfortable and easy. They were two sides of the same coin and held a mutual respect for each other. If Red didn't return his love, Sans wasn't sure he could handle it... and so he kept his mouth shut and kept his love for Red clamped down and hidden deep within his soul. He'd take what he could of Red's affection, and that would have to be enough.  
  
He was distracted from his thoughts by the door upstairs opening and closing and he grinned, turning off the radio and looking up to watch his sharp-toothed double rush down the stairs. "hey there, sweetheart. sorry i kept ya waiting," Red said breathlessly, and as always, the pet name sent a thrill through Sans, though he knew it shouldn't. Red used that pet name for his Frisk as well.  
  
"it's not like you were late or anything," Sans replied with a soft laugh. "i just got down here early."  
  
"still..." Red grumbled, but then shook his skull, expression firming as he picked up the collar he liked to have Sans wear during their play. It was a solid line for them. Once Sans was wearing the collar, they stayed in their roles unless one of them needed to use their safe words. Sans stood, turning and lifting his chin to allow Red to fix the collar around his neck, their sign that he was ready to start.  
  
Once the solid weight of the collar was in place, Red hummed softly before ordering Sans to strip. Sans did so without a word, tucking his shoes and socks neatly under the desk and draping his jacket, t-shirt, and shorts over his chair to keep them all out of the way. Red let out a pleased sound that had Sans flushing in pleasure. "good boy," Red purred. "come here," he ordered, moving to stand next to a recently installed apparatus that they hadn't yet used.  
  
It was a simple piece consisting of three metal poles. The main pole was a simple bar that affixed to the floor and ceiling for stability. A thick, short chain that looked like it would affix to his collar was attached at neck hight and an additional two straps that looked like they were meant to bind his spine to the pole were bolted on. The rest of the pole was wrapped in some sort of cushioning, likely to protect his bones from the hard steel. The other two bars were affixed at ankle and shoulder height and had fur lined leather restraints attached to them.  
  
Red was quick to position Sans how he wanted, before binding him to the apparatus. Once he was fully secured, Sans tugged testingly at each restraint, finding himself barely able to move, though nothing was uncomfortable. Red waited patiently until Sans met his eyelights and murmured the word 'green', signalling that he was okay. Red relaxed a little before smirking and picking up a blindfold. There was a moment where he waited to see if Sans would reject it, but Sans simply closed his sockets, and Red secured the blindfold, cutting off Sans' sight completely.  
  
"there we go, pet. yer perfectly trussed up," Red purred, and Sans turned his face toward's Red, humming softly. "now, i noticed somethin' last time we played. something ya never told me, and i have ta wonder why. did ya not trust me enough ta tell me? or did ya just not realize it was somethin' ya were inta?" Red asked, trailing his claw-like phalanges teasingly along Sans' arm.  
  
Sans made a soft confused sound and Red growled, "use yer words, pet."  
  
"of course i trust you... more than anyone," Sans said softly. "i'm... not entirely sure what you mean, to be honest," he added, and Red let out a thoughtful hum, casually stroking Sans' ribs, phalanges thoughtlessly plucking at bone and making Sans gasp and try fruitlessly to arch into the contact.  
  
"hm... so you really hadn't noticed," he murmured thoughtfully, continuing to play Sans' body like a finely tuned instrument. "well then, i suppose this is to be another experiment day. i want to see if what i noticed the other night actually holds true. colour?"  
  
"green," Sans replied, and Red let out a pleased hum. The next moment, Sans gasped sharply as claws raked down his ribs, leaving a tingling burn in their wake. The sting was soothed moments later by Red's tongue licking at the scratches, and the wet warmth pulled a soft moan from him, the softer skeleton already starting to breathe a bit heavier from the stimulation. Red licked his way up to Sans' clavicle where he nipped at the bone just hard enough to sting before licking at the bone, and Sans moaned again, teeth parted and tongue lolling a little as Red kept up the pattern of nipping and licking.  
  
After a little bit of that, Red pulled back and let out a soft whistle-like sound. "fuck, pet, that really got ya, huh?" he muttered, reaching out and stroking Sans' skull. Sans hummed and nuzzled into the gentle hand. "how would ya feel if i really bit ya? if i sunk my teeth in deep enough to draw marrow and leave a permanent mark on yer bones?" he growled softly, and Sans keened quietly at the thought, his magic solidifying into a cunt between his legs.  
  
"green, green, fuck, _please_ ," Sans begged and Red let out a startled curse, one hand moving to rub at Sans' cunt, the tip of one clawed phalanx rubbing and flicking Sans' clit while he wrapped his other arm around Sans, nuzzling at his collar bone and licking at the bone. Almost tentatively, he closed his teeth around the sensitive bone, digging in harder than before. Sans let out a tiny, pained sound, but he didn't even utter the word yellow. Instead, what followed the little sound was, "please, harder," moaned softly in his ear.  
  
Red complied, sinking his teeth in deep enough for the marrow to start leaking out when he pulled them free to lap at the fresh wounds. Sans whined, hips twitching into Red's touch, and he responded by plunging two phalanges into Sans' cunt, his thumb rubbing at his clit as he roughly fingered the bound skeleton. He bit Sans again, biting hard at different bones and lapping at the resulting wounds after, and each time, the sounds Sans made just got more and more desperate, begging Red to bite harder until with a strained shriek, Sans came harder than he'd probably ever came in his life.  
  
When Sans slumped limply in his bonds, Red let out a soft, vehement curse, turning Sans' soul blue to hold him up while he got the bindings off the smaller skeleton. Worry for Sans made his soul pulse, wondering if he'd gone too far. Sans had never passed out like that after a session, after all. Once all the bindings were off and the collar was unclipped, Red gently scooped his sub up and carried him over to the bed they'd tucked away in the corner specifically for after care. Red then grabbed the water basin and cloth that had been prepared earlier and started carefully cleaning the deep marks he'd left in Sans' bones. Some of the bites were much deeper than he'd meant to go, having been caught up in the moment, and he winced. The deepest ones were almost punctured all the way through. Any harder and he would have broken the bone.  
  
He was extra careful with those ones, cleaning them delicately before applying a healing cream to each and every wound he'd left. It was as he was just finishing up that Sans finally came to, socket lids fluttering open to reveal hazy eyelights. "there ya are, sweetheart," Red murmured softly, petting Sans' skull with his clean hand. Sans made a soft, muzzy sound, nuzzling into Red's hand happily, and Red noted with a start that Sans had gone pretty deep this time. "what do ya need, sans?" he asked gently, and Sans made a questioning sound. "i know ya feel pretty good right now, but it's time ta come back, sansy. i know yer in there, so what do ya need?"  
  
"...you. hold me...?" Sans replied after a moment, and Red smiled and nodded, shucking off his jacket and shirt before climbing onto the bed with Sans, cuddling him close and stroking his skull with one hand and his spine with the other. Sans let out a soft, contented sound, relaxing fully into Red. "i love you..." he murmured softly before his breathing evened out as he dozed off. Red let him, though even if he wasn't utterly shocked by the confession, he'd stay stubbornly awake anyway to keep an eye on the slightly smaller skeleton.  
  
When Sans woke again a while later, he seemed a bit more himself, eyelights once more solid white dots in his sockets. He groaned softly, nuzzling into Red's ribs absently which made the fanged skeleton chuckle softly. "how ya doin', sweetheart?" he asked softly.  
  
"kinda achy. shouldn't be surprised seeing as you bit me so hard," Sans muttered, shifting to poke at his injuries, though Red didn't let him, hand catching Sans by the wrist.  
  
"don't do that, sweetheart. i did a lot more damage than i meant to, and you might aggravate them," Red murmured, regret in his tone. He really hadn't meant to actually hurt Sans.  
  
Sans' sockets widened when he took a look at Red's face and he pulled away a little so Red could see him clearly. "blue," he stated firmly, and Red jerked, looking up at him, startled.  
  
"...ya sure yer okay?" he asked softly, subdued, and Sans nodded. Red reached up with shaking hands, undoing the collar around Sans' neck, letting it drop to the bed carelessly between them. With the playing field evened by the lack of the collar, Sans gathered Red to him, returning the soothing gestures from before, petting Red's skull and stroking down his back.  
  
"red, i meant what i said. i trust you more than anyone. you bit me to hell and back, yeah, but you didn't do anything i didn't want. i asked for it. literally. fuck, you taught me something about myself i didn't even know today... but i think we also learned something about you, too, and i think we need to have a long talk before we engage in pain play again, if we do. i'd like to, of course, but not if you're just gonna cause yourself emotional damage doing that for me," Sans murmured, continuing to pet Red while he spoke.  
  
Red, who'd snuggled into Sans as best he could without risking jostling the bite wounds too much, looked up in shock. "i... yeah... fuck, i enjoyed it while i was doing it, but... that's gonna take forever ta heal... and they're gonna scar pretty bad, too..."  
  
"then we find methods of pain play that won't leave lasting wounds. as i said, this is something we're going to need to talk about... but later, when we are both feeling okay again. as for the potential future scars... would you be upset if i told you i'm looking forward to baring some permanent mark from you?" Sans asked, looking away shyly. Red let out a startled bark of a laugh at that, sitting up slightly and moving the collar off the bed in order to pull Sans close.  
  
"fuck, yer such an asshole," he growled goodnaturedly, and Sans laughed, snuggling in to cuddle more. He hadn't _really_ been ready to take off the collar and they both knew it. However, in the current situation, they'd needed to be on even footing, just Sans and Red, not a sub and his dom. Silence fell over the pair for a short while, just cuddling and listening to each other breathing. Red broke it some time later with a soft sound before speaking. "hey, sans?"  
  
"mm?"  
  
"i love ya, too."

**Author's Note:**

> so, their safe word system is green/yellow/blue. i chose 'blue' as the end-all word because, well, Red is UF!Sans' name, and it's a nod to Sans' in-game joke about blue stop signs. haha
> 
> Sans lifting his chin for the collar is, of course, him saying he's ready to start a scene. him saying 'blue' is the end all if the scene is getting too much, but it's also his way of telling Red that he's okay after a scene and during the aftercare phase. in this case, though, Red had pushed beyond his own limits as a dom without realizing until after and he needed more active aftercare. tending to Sans wasn't enough that time, so Sans broke scene before he was ready to in order to help Red. they finish their aftercare together in a different way than normal, but both are fine in the end.


End file.
